Colorimetric Analysis

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Colorimetric Analysis: Manganese in Steel

Chemistry 2272F
Nov 8, 2012

Introduction
The goal of the experiment is to determine the percentage of Mn in an unknown metal sample by means of colorimetric analysis.
First stock solution of KMnO4 with known concentration was diluted and then carried to spectrometer for analysis. The peak with highest absorbance was taken as λmax. Then the molar extinction coefficient is calculated by plugging the value into the Beer-Lambert equation. Then the concentration of Mn2+ in unknown sample can be determined by scanning it in the spectrometer.1

UV/VIS Spectrophotometry is used to determine the absorption or transmission of UV/VIS light (180 to 820 nm) by a sample. A spectrometer is used in the process. Inside a spectrometer light from a source is separated into narrow bands by wavelength, pass through the sample and then measured by the detector.2 In this experiment UV/VIS Spectrophotometry is used to determine the absorbance of MnO4- ion in the solution.

Beer-Lambert law states that absorbance is proportional to the concentration of the absorbing species. The equation is A=ԐbC, where A is the absorbance, b is the path length, Ԑ is the molar extinction coefficient and C stands for concentration.2 In the experiment with the absorbance of MnO4- ion in stock solution determined by UV Vis spectrophotometry in part A and the absorbance in unknown sample was determined in part B, the concentration of Mn2+ can be calculated.

Experimental
There was no change in the experiment. 1
Results and Discussion (Sample # 2061)
Part A
Dilution of KMnO4
10mL transferred to 100mL volumetric flask: 9.9958mL x 0.003998M/100mL

10mL transferred to 100mL volumetric flask: 9.9958mL x 0.003998M/100mL

20mL transferred to 100mL volumetric flask: 9.9958mL x 2x 0.02M/100mL 20mL transferred to 100mL volumetric flask: 9.9958mL x 2x 0.02M/100mL

The wavelength used was 526nm.
A=ԐbC
Ԑ=A/bC= 0.935455/1x0.00039963=2340.8027 L...
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